Hello Everyone. I am currently working on a project for my lab at school which will calibrate our collection electronics on a physics experiment. The apparatus emits low current(nanoamp or less range), and has typical pulse widths of roughly 10ms. In order to calibrate this I need to build a circuit that can produce these kinds of signals. I am assuming I need to use a current controlling DAC like the Maxim MAX5661 and filter it with some low pass op-amp circuits and then use a transformer to get the desired current. Everything on the microcontroller and digital side of the DAC I think I know what to do. However, if I am going to be putting out current signals with amplitude in the nanoamp range and hopefully resolution in the picoamp or better range, should I use a transformer to do this(I need to keep the noise out obviously)? If so, can anyone suggest a good source for a transformer like this (since the DAC works in the milliamp range I need something with a large ratio, like 10000:1 or better I suppose)? Also if anyone has any suggestions on how to transform the signal after it comes out of the DAC it would be much appreciated.

 

It may not be as hard as you think. Try using a bridge with match resistances (can be purchased as a package). You feed your know current (from the DAC) through one side of the bridge and your unknow current through th other. Monitor the voltage across the bridge and adjust your output of the unit you are calibrating till you get a null. The only difficulty it knowing the exact current of the DAC output. You may need to build a unit to calibrate this. ooopppsssss going around in circles.